(1) Field of the Invention
This invention relates to a method of mounting a semiconductor device and etc., and more particularly relates to a solder carrier for simultaneously forming bumps on a plurality of small precise connecting terminals, each bump being made of a predetermined constant quantity of solder.
(2) Description of the Prior Art
As regards conventional methods of forming bumps for the purpose of connecting terminals in a method of mounting semiconductors, there have been known an evaporated solder bump method in which the bumps are formed by evaporating solder while using metal masks, and a solder-plating bump method (CCB Method: Controlled Collapse Bonding Method) in which the bumps are formed by solder-plating conducted while using solder resist masks.
Furthermore, a method is disclosed (Japanese Patent Laid-Open No. 58-35935) in which an organic insulating sheet having both through-holes formed by a punching method and solder balls filling the through holes is directly located on the bump portions of a semiconductor device, which sheet is then heated and bonded onto the bump portions of the semiconductor device through the molten solder secured to the bump portions. In this method, the insulating sheet, which serves as a ball carrier, per se is mounted on a semiconductor device, too.
A method is also disclosed (Japanese Patent Laid-Open No. 60-234396) in which a solder material is welded to pads by heating and fusing a plate-shaped jig having little wettability regarding solder and having conical or quadrangular pyramid-like grooves formed on the surface thereof which grooves are filled with solder paste.
The evaporated solder method has such shortcomings that unsuitable variation in the amount of applied solder occurs and that, since the vapor pressure of Sn is high, in a case of obtaining a required composition in which the proportion of Sn is high, for example, Pb/Sn=4/6, several tens of hours become necessary. On the other hand, in the solder-plating method, a degree of variation in amount of applied solder becomes higher, and a large number of manufacturing steps are required.
Furthermore, in the method described above in which an organic sheet is used the following problems arise:
(1) Since a puncher is used, it is necessarily difficult to realize a high-density distribution of holes.
(2) Since the solder balls need to be supplied to a plurality of small through holes bored in the organic sheet without dropping therefrom, it becomes difficult to produce the carrier sheets.
(3) It is difficult to manufacture solder balls uniform in both shape and dimensions. Even if it is possible, the solder balls are apt to drop from the through holes and are therefore difficult to handle since the sheet employed is a thin film (100 .mu.m in thickness) sheet.
(4) Even if a polyamide sheet having excellent heat resistance is used as the organic sheet, when the sheet is heated up to the temperature at which the solder melts, residual strain occurring at the time of forming the holes is relieved to cause deformation of the sheet because of thin thickness of the sheet, which deformation makes it impossible to correctly place the sheet in place.
Problems therefore arise in this method if used as a solder carrier for forming solder balls mounted on a semiconductor device in which high precision and high density are required.
Furthermore, in a method in which the conical or quadrangular pyramidal grooves are formed in a jig made of a material, such as polytetra-fluoroethylene or stainless steel, having little wettability regarding solder in which jig a material for soldering fills the grooves, it is difficult to insert a constant amount of solder to the jig. The solder to be inserted must be fused, but such fused solder becomes spherical in shape due to the surface tension caused by the inferior wettability of the jig. Therefore, if excess parts of the solder that projects over the surface of the jig are removed by a sqeegee or the like, even a part of the fused solder filling the grooves in the form of a sphere will be also removed together with the excess solder. It is therefore difficult to supply a constant amount of solder to these conical or quadrangular pyramidal grooves.